Bis(tridentate)cobalt(III) complexes with diethylenetriamine and 4-Methyldiethylenetriamine [2,2'-Methyliminodi(ethylamine)]: assignment of geometric configurations by 1H and 13C N.M.R. spectroscopy

Abstract

The new complexes symmetrical-facial-[Co(medien)₂]³⁺ and s-fac- [Co(dien)(medien)]³⁺ have been isolated. The ¹H NMR spectra of these complexes, the s-far, u-far and meridional isomers of [Co(dien)₂]³⁺, and u-fac-[Co(daes)₂]³⁺ show different splittings of the NH₂ proton resonances [dien = diethylenetriamine, medien = 4- methyldiethylenetriamine or 2,2'-methyliminodi(ethyl-amine), daes = di(2-aminoethyl) sulphide or 2,2'-thiodi(ethylamine)]. These splittings depend on the geometries of the complexes (different numbers of stereochemically distinct NH₂ groups), the particular chelated ligands (splittings due to coupling between the two protons on each NH₂ may vary with chelate ring conformational mobility), and the counter-anions (different extents of ion- association through hydrogen bonding). Thus NH₂ proton resonance signals may not always provide a reliable method for establishing molecular geometries. In contrast, the ¹³C NMR spectra of all these complexes are completely diagnostic of the detailed geometries, and most of the resonances observed have been assigned to particular carbon atoms.